Method for controlling shape measuring apparatus

ABSTRACT

A method for nominal scanning measurement includes allowing a user to select a shape of an object to be measured from a geometric shape menu prepared in advance, allowing the user to input, according to the selected geometric shape, a parameter to specify the geometric shape, allowing the user to select a measurement path from a measurement path menu prepared in advance, allowing the user to input, according to the selected measurement path, a parameter to specify the measurement path, calculating, based on the selected geometric shape, the input parameter of the geometric shape, the selected measurement path, and the input parameter of the measurement path, measurement points on a workpiece and a normal line direction at each of measurement points using a calculation formula prepared in advance, and calculating a path for scanning measurement to move while scanning a sequence of the measurement points.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2015-111960, filed on Jun. 02, 2015, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling a shapemeasuring apparatus.

2. Description of Related Art

There has been known a shape measuring apparatus which measures a shapeof an object to be measured by moving a stylus head while scanning asurface of the object to be measured (for example, JP 2008-241420 A, JP2013-238573 A, and JP 2014-21004 A).

To perform scanning measurement, a path for the scanning measurementneeds to be generated.

The device disclosed in JP 2008-241420 A converts a design data (forexample, non-uniform rational B-spline (NURBS) data) based on CAD datainto a group of polynomials curves in a predetermined degree.

CAD data (for example, NURBS data) including path information isreceived from an external CAD system or the like, and the CAD data isconverted into data of a group of points. The data at each point iscombined data of coordinates (x, y, z) and normal line directions (P, Q,R). (That is, the data indicates (x, y, z, P, Q, R).)

In this description, the data having information of (x, y, z, P, Q, R)is referred to as contour point data.

Next, the coordinates at each point are offset by a predetermined amountin the normal line direction. (The predetermined amount is,particularly, a stylus head radius r—an amount of deflection Ep.) Thedata of a group of points calculated in this manner is referred to as“offset contour point data”.

Then, the offset contour point data is converted into a group ofpolynomials curves in a predetermined degree.

Here, it is assumed that the polynomials is a cubic function, and thecurves are parametric cubic curves (PCC).

Based on the PCC curve, a path to measure a workpiece is generated.

Furthermore, a PCC curve is divided into a group of divided PCC curves.A speed curve is calculated from the group of divided PCC curves, andthen, a moving speed (moving vector) of a probe is calculated. (Forexample, a moving speed (moving vector) of a probe is set based on acurvature of each segment of the group of divided PCC curves or thelike.)

The probe is moved according to the moving speed calculated in the abovemanner, and a stylus head is moved while scanning a surface of an objectto be measured (passive nominal scanning measurement: note that the word“nominal” in this description means scanning along a predeterminedtrajectory calculated in advance based on design data of an object.).

Furthermore, there has been known a method to perform scanningmeasurement while correcting a trajectory by continuously calculating adeflection correcting vector so that an amount of deflection of a probebecomes constant (JP 2013-238573 A).

In this description, such scanning is referred to as “active nominalscanning measurement”.

Moreover, there has been known a method to perform scanning measurementwhile generating a trajectory without using design data (autonomousscanning measurement, for example JP 5089428 B).

As described above, there are three measurement methods of passivenominal scanning measurement, active nominal scanning measurement, andautonomous scanning measurement, and each of them has merits anddemerits.

For example, although all workpieces could be measured by the autonomousscanning measurement, the autonomous scanning measurement takes a longtime.

For example, a moving speed of a probe in the autonomous scanningmeasurement is about 10 mm/sec to 15 mm/sec, and a moving speed of aprobe in the nominal scanning measurement is about 50 mm/sec to 100mm/sec. Thus, it is expected that the autonomous scanning measurementtakes time about ten times longer than the nominal scanning measurement.

SUMMARY OF THE INVENTION

Nominal scanning measurement has an excellent measurement efficiency,but needs a rather high-performance computer (graphic workstation) toperform processing, such as converting CAD data or the like into PCCcurves. If a user frequently uses a coordinate measuring machine whichmeasures a number of workpieces having complicated shapes, the user caninvest in an expensive computer (graphic workstation).

However, on the other hand, there are demands from a user whooccasionally needs to simply measure a unique object, such as a trialproduct or a special order product.

Thus, it is desirable that nominal scanning measurement is to be easilyused by a light user without CAD data or a high-performance PC.

In an embodiment of the present invention, a method for controlling ashape measuring apparatus which includes a probe having a stylus head ata tip and a moving mechanism to move the probe, and measures a shape ofa workpiece by detecting contact between the stylus head and a surfaceof the workpiece, the method includes:

allowing a user to select a shape of an object to be measured from ageometric shape menu prepared in advance;

allowing the user to select a measurement path from a measurement pathmenu prepared in advance;

calculating, based on the selected geometric shape and the selectedmeasurement path, measurement points and a normal line direction at eachof the measurement points on the workpiece using a calculation formulaprepared in advance; and

calculating a path for scanning measurement to move while scanning asequence of the measurement points, and performing the scanningmeasurement to scan the path for the scanning measurement.

In an embodiment of the present invention, the method preferablyincludes:

allowing the user to input, according to the selected geometric shape, aparameter to specify the geometric shape;

allowing the user to input, according to the selected measurement path,a parameter to specify the measurement path; and

calculating, based on the selected geometric shape, the input parameterof the geometric shape, the selected measurement path, and the inputparameter of the measurement path, measurement points and a normal linedirection at each of the measurement points on a workpiece using acalculation formula prepared in advance.

In an embodiment of the present invention, the geometric shape menupreferably includes, at least, a sphere, a columnar body, a cone body,and a plane.

In an embodiment of the present invention, the measurement path menupreferably includes, at least, a spiral and a sine curve.

In an embodiment of the present invention, a control program for a shapemeasuring apparatus causing a computer to execute a method forcontrolling the shape measuring apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an entire configuration of a shapemeasuring system;

FIG. 2 is a functional block diagram of a motion controller and a hostcomputer;

FIG. 3 is a diagram illustrating a functional configuration of asimplified nominal scanning measurement part program;

FIG. 4 is an entire flowchart for explaining operations of simplifiednominal scanning measurement;

FIG. 5 is a flowchart illustrating a procedure of a preparation step(ST100);

FIG. 6 is a flowchart illustrating a procedure of a selection input step(ST200);

FIG. 7 is a diagram exemplifying a selection menu;

FIG. 8 is a diagram exemplifying a selection menu;

FIG. 9 is a diagram exemplifying an input screen;

FIG. 10 is a diagram exemplifying a selection menu;

FIG. 11 is a diagram exemplifying an input screen;

FIG. 12 is a diagram illustrating spherical coordinates;

FIG. 13 is a diagram illustrating that scanning measurement is performedto a spherical workpiece with a spiral path;

FIG. 14 is a diagram exemplifying an input screen; and

FIG. 15 is diagram illustrating that scanning measurement is performedto a spherical workpiece with a sine curve path.

DETAILED DESCRIPTION Summary of the Present Invention

It has been described that there are demands, for example, from a userwho occasionally needs to simply measure a unique object, such as atrial product or a special order product.

Analyzing these demands, a point to be measured is a geometric shape,such as a part of a plane, a part of a sphere, a part of a cylinder, ora part of a cone, or can be mostly replaced with a geometric shape.

Thus, to perform nominal scanning measurement, a menu for nominalscanning measurement using approximation functions, instead of CAD data,is prepared in advance. The demands from a light user can be satisfiedwithout CAD data or a high-performance computer (graphic workstation)accordingly.

Embodiments of the present invention will be illustrated and describedwith reference to reference signs assigned to elements in the drawings.

First Exemplary Embodiment

FIG. 1 is a diagram illustrating an entire configuration of a shapemeasuring system 100.

The basic configuration of the shape measuring system 100 has beenknown, but will be briefly described.

The shape measuring system 100 includes a coordinate measuring machine200, a motion controller 300 which controls the drive of the coordinatemeasuring machine 200, and a host computer 500 which controls the motioncontroller 300 and executes necessary data processing.

The coordinate measuring machine 200 includes a base 210, a movingmechanism 220, and a probe 230.

The moving mechanism 220 includes a gate type Y slider 221, an X slider222, a Z axis column 223, and a Z spindle 224. The Y slider 221 isprovided slidably on the base 210 in a Y direction. The X slider 222slides along a beam of the Y slider 221 in an X direction. The Z axiscolumn 223 is secured to the X slider 222. The Z spindle 224 moves upand down inside the Z axis column 223 in a Z direction.

A driving motor (not illustrated) and an encoder (not illustrated) arefixed on each of the Y slider 221, the X slider 222, and the Z spindle224.

Drive control signals from the motion controller 300 control the driveof the driving motors.

The encoder detects a moving amount of each of the Y slider 221, the Xslider 222, and the Z spindle 224, and outputs the detection value tothe motion controller 300.

The probe 230 is attached to the lower end of the Z spindle 224.

The probe 230 includes a stylus 231 and a supporting part 233. Thestylus 231 has a stylus head 232 at a tip side (-Z axis direction side).The supporting part 233 supports a base end side (+Z axis directionside) of the stylus 231.

The stylus head 232 has a spherical shape and is brought into contactwith an object W to be measured.

When an external force is applied to the stylus 231, that is, when thestylus head 232 is brought into contact with an object to be measured,the supporting part 233 supports the stylus 231 so that the stylus 231is movable in the directions of the X, Y, and Z axes within a certainrange. The supporting part 233 further includes a probe sensor (notillustrated) to detect a position of the stylus 231 in each axisdirection.

The probe sensor outputs the detection value to the motion controller300.

(Configuration of the Motion Controller 300)

FIG. 2 is a functional block diagram of the motion controller 300 andthe host computer 500.

The motion controller 300 includes a PCC acquisition unit 310, a counter320, a path calculation unit 330, and a drive control unit 340.

The PCC acquisition unit 310 acquires PCC curve data from the hostcomputer 500.

The counter 320 measures an amount of displacement of each slider bycounting detection signals output from the encoder, and measures anamount of displacement of the probe 230 (the stylus 231) by countingdetection signals output from each probe sensor.

From the measured displacement of the slider and the probe 230, acoordinate position PP (hereinafter, referred to as a probe position PP)of the stylus head 232 is obtained. Furthermore, from the displacement(the detection values of the probe sensor (Px, Py, Pz)) of the stylus231 measured by the counter 320, an amount of deflection (an absolutevalue of a vector Ep) of the stylus head 232 is obtained.

The path calculation unit 330 calculates a movement path for the probe230 (the stylus head 232) to measure a surface of an object to bemeasured with the probe 230 (the stylus head 232), and calculates avelocity component vector (path velocity vector) along the movementpath.

The path calculation unit 330 includes functional units to calculate apath according to measurement methods (measurement modes). Specifically,there are four methods of passive nominal scanning measurement, activenominal scanning measurement, autonomous scanning measurement, and pointmeasurement.

The measurement methods will be described later as needed.

The drive control unit 340 controls the drive of each slider based onthe moving vector calculated by the path calculation unit 330.

Note that, a manual controller 400 is connected to the motion controller300.

manual controller 400 includes a joystick and various buttons, receivesa manual input operation from a user, and transmits the user'soperations instruction to the motion controller 300.

In this case, the motion controller 300 (the drive control unit 340)controls the drive of each slider in response to the user's operationsinstruction.

(Configuration of the Host Computer 500)

The host computer 500 includes a central processing unit (CPU) 511 and amemory, and controls the coordinate measuring machine 200 through themotion controller 300.

The host computer 500 further includes a storage unit 520 and a shapeanalysis unit 530.

The storage unit 520 stores measurement data obtained by measurement,and a measurement control program to control a whole measurementoperation.

In the present exemplary embodiment, a part program for the simplifiednominal scanning measurement is included as a part of the controlprogram.

The part program for the simplified nominal scanning measurement isroughly divided into two function units as illustrated in FIG. 3. One isa geometric shape selection unit, and the other is a path patternselection unit.

Examples of operations controlled by the selection units will bedescribed later.

A part program for simplified nominal scanning measurement is too longto repeat, and is referred to as a “simplified measurement partprogram”.

The shape analysis unit 530 calculates surface shape data of the objectto be measured based on the measurement data output from the motioncontroller 300, and performs shape analysis to calculate error ordistortion of the calculated surface shape data of the object to bemeasured.

The shape analysis unit 530 further performs arithmetic processing, suchas conversion of various parameters input to perform the simplifiednominal scanning measurement into PCC curves.

The CPU 511 executes the measurement control program, and thus themeasurement operations of the present exemplary embodiment isimplemented.

An output device (a display or a printer) and an input device (akeyboard or a mouse) are connected to the host computer 500 as needed.

(Description of the Measurement Operation)

The measurement operations of the present exemplary embodiment will bedescribed.

The present exemplary embodiment is to perform nominal scanningmeasurement without design data, and which is referred to as “simplifiednominal scanning measurement”.

Procedures of the present exemplary embodiment are illustrated in FIG. 4and described in order.

FIG. 4 is a flowchart for explaining operations in the simplifiednominal scanning measurement.

Note that, the goal is to perform the scanning measurement to a spheresurface with a spiral path illustrated in FIG. 13.

First, preparation necessary for scanning measurement is performed (apreparation step ST100).

The preparation step (ST100) is performed by the host computer 500.

FIG. 5 illustrates the procedures of the preparation step (ST100).

As the preparation step (ST100), first, a selection input step (ST200)which allows a user to select or input necessary information isperformed.

The selection input step (ST200) is detailedly illustrated in FIG. 6.

As the selection input step (ST200), a measurement method is selected bythe user (ST210). For example, a selection menu illustrated in FIG. 7 ispresented to the user.

The menu of measurement methods includes passive nominal scanningmeasurement, active nominal scanning measurement, autonomous scanningmeasurement, and point measurement, and further includes “simplifiednominal scanning measurement” in the present exemplary embodiment.

Here, it is assumed that the user selects the “simplified nominalscanning measurement” (ST220: YES).

Since the “simplified nominal scanning measurement” is selected, thesimplified-measurement part program allows the user to select a shape ofa measurement point from a prepared geometric shape menu (ST230).

For example, a selection menu illustrated in FIG. 8 is presented to theuser.

In this description, the shape menu includes a sphere, a cylinder, acone, and a plane. In addition, a prism (polygonal prism) and a pyramid(polygonal pyramid) may be included. Furthermore, whether the shape tobe measured is an inner surface or an outer surface is selected.

Here, it is assumed that a “sphere” and an “outer surface” are selected.

When the geometric shape is selected, the user is requested to input aparameter necessary for specifying the detail of the selected geometricshape (ST240).

Here, a sphere is selected, and a screen to input, for example, centercoordinates (x, y, z), and a radius r in an input screen illustrated inFIG. 9 is presented. Thus, the geometric shape of the object to bemeasured is obtained.

Next, the simplified-measurement part program allows the user to selecta pattern of a measurement path.

The simplified-measurement part program allows the user to select ameasurement path from a prepared measurement path menu (ST250).

For example, a measurement path menu illustrated in FIG. 10 is presentedto the user. Here, a path menu includes a fixed height, a spiral, and asine curve.

The fixed height means that a z-coordinate is fixed, and the path menumay include, in addition, a fixed x-coordinate, and a fixedy-coordinate, and may allow a user to input an inclined scanningsection.

Furthermore, the path menu may be prepared for each geometric shape.

For example, a path menu to perform measurement throughout an object tobe measured by zigzagging on a plane may be prepared for a workpiecehaving a flat surface, such as a plane, a prism, and a pyramid.

Here, it is assumed that a spiral is selected.

When the measurement path is selected, the user is requested to input aparameter necessary for specifying the detail of the selected path(ST260).

Here, since a spiral is selected as the measurement path, a screen toinput information, such as a start point (φ_(xy0), θ_(z0)), an end pointθ_(zf), the number of turns i, and the number of sampling points N, ispresented (FIG. 11).

The angles are defined, for example, as illustrated in FIG. 12.

The angle φ is an angle from an X axis in an XY plane.

The angle θ is an angle from Z axis in a ZY plane.

The number of turns i may include not only integers but also decimalnumbers, such as 1.5 and 2.25, and which can omit to input the value pof the end point.

With these steps, the geometric shape of the workpiece which is theobject to be measured and the information on the user's desired scanningpath are obtained.

Thus, the selection input step (ST200) is terminated.

Following the selection input step (ST200), a shape calculation step(ST300) is performed.

The shape calculation step (ST300) is performed by a shape analysis unit530 based on the information obtained in the selection input step(ST200).

In the shape calculation step (ST300), measurement points (a pointsequence) on the workpiece are calculated using prepared calculationformulae.

Since the workpiece is a sphere, using the spherical coordinates of FIG.12 and setting the center coordinates of the sphere as an origin, themeasurement points (a point sequence) (r, θ_(xy), θ_(z)) on theworkpiece is indicated as follows:

φ_(xy)=φ_(xy0)+[360i×{(k−1)/(N−1)}]

θ_(z)=θ_(z0)−[(θ_(z0)−θ_(zf))×{(k−1)/(N−1)}]

Here, k indicates the k-th sampling point (k=1,2, 3 . . . N).

The measurement points (point sequence) (r, φ_(xy), θ_(z)) are obtained,and contour point data (x, y, z, P, Q, R) is obtained as follows(ST400).

In other words, the spherical coordinates are converted into orthogonalcoordinates with the following calculation formulae:

x=rsinθcosφ

y=rsinθsinφ

z=rcosθ

Furthermore, setting the center of the sphere as an origin, the originand each of the measurement points (x, y, z) are combined, and therebythe normal line directions (P, Q, R) at each of the measurement pointsare obtained.

Thus, the coordinates (x, y, z) and the normal line directions (P, Q, R)are obtained for each measurement point, which means that an equivalentto the contour point data is obtained.

Once the contour point data is obtained, the technique for convertingthe data into a PCC curve is known (JP 2008-241420 A, JP 2013-238573 A,and JP 2014-21004 A).

To be briefly described, the contour point data is offset in the normalline direction by a predetermined amount, and then a PCC curve iscalculated (ST500).

With the above procedures, the path for the nominal scanning measurementis obtained. Thus, the preparation step (ST100) is terminated.

Since the preparation step (ST100) is terminated, the host computer 500instructs the motion controller 300 to perform the nominal scanningmeasurement (ST610).

The nominal scanning measurement itself has been well known, and thedetails are omitted.

The brief description is as follows:

The PCC curve is transmitted to the motion controller 300 andtemporarily stored in the PCC acquisition unit 310.

The path calculation unit 330 generates a path to measure the workpiecebased on the PCC curve.

The path calculation unit 330 generates a path according to themeasurement method.

Here, it is assumed that active nominal scanning measurement is to beperformed and a path for the active nominal scanning measurement isgenerated.

(Note That, Paths Generated For the active Nominal Scanning Measurementand the Passive Nominal Scanning Measurement are the Same.)

The path calculation unit 330 sets, based on the curvature of thedivided PCC curve, the moving speed of the probe 230, and determines themoving direction and the moving speed (velocity vector) at each point onthe PCC curve. The movement of the probe 230 according to the movingvector implements the nominal scanning measurement.

Furthermore, in the case of the active nominal scanning measurement, avector in the normal line direction (deflection correcting vector) isgenerated so that the amount of deflection Ep becomes constant, and atrajectory correction direction (trajectory correction vector) tocorrect the deviation between the center coordinates and the path of thecurrent stylus head 232 is generated. Then, a combined velocity vector,which is obtained by combining the velocity vector, the deflectioncorrecting vector, and the trajectory correction vector, is generated.

The drive control unit 340 supplies drive signals to the coordinatemeasuring machine 200 according to the combined velocity vector.

Thereby, the coordinate measuring machine 200 measures the workpiece bythe active nominal scanning measurement.

The drive signals from the motion controller 300 drive the coordinatemeasuring machine 200, and thus the active nominal scanning measurementis performed.

The coordinate measuring machine 200 feedbacks detection values (a probesensor detection value and an encoder detection value) to the hostcomputer 500 through the motion controller 300.

The data obtained by the measurement is stored in the storage unit 520(ST620). When all of the measurement points on the path are measured(ST630: YES), the measurement is terminated.

With the above described present exemplary embodiment, it is possible toperform nominal scanning measurement without a CAD system or ahigh-performance PC.

Modified Example 1

For reference, the case in which a “sine curve” is selected in ameasurement path selection (ST250) will be described. FIG. 15illustrates an example of a sine curve path for scanning measurement.

When a “sine curve” is selected as a measurement path, a screen to inputinformation, such as a start point (θ_(zy0), θ_(z0)), amplitude (θ_(zH),θ_(zL)), the number of turns i, the number of sampling points N, ispresented (FIG. 14).

Note that, θ_(zH) indicates the maximum value of θ_(z), and θ_(zL)indicates the minimum value of θ_(z).

With the information, measurement points (a point sequence) (r, φ_(xy),θ_(z)) on a workpiece is indicated as follows:

φ_(xy)=φ_(xy0)+[360×{(k−1)/(N−1)}]

θ_(z)=(θ_(zH)+θ_(zL))/2±{(θ_(zH)−θ_(zL))/2}sin[360i×{(k−1)/(N−1)}]

If an object to be measured is a sphere, a spherical coordinates systemis used, and if an object to be measured is a cylinder, a cylindricalcoordinate system is used. Other processing is the same as aboveembodiment.

Modified Example 2

When the shape parameter is input (ST240), the center coordinates of thesphere have been input (FIG. 9). However, a menu of “automatic settingof center coordinates” may be added based on the assumption thataccurate center coordinates in a machine coordinate system are notimmediately obtained.

If it has been known that the shape is a sphere, the center coordinatescan be calculated by measuring some points on a workpiece.

When the “automatic setting of center coordinates” is selected, thecenter coordinates may be obtained by, for example, preliminarilymeasuring some points on the workpiece by point measurement. The pointmeasurement may be performed automatically or manually by a user.

Note that, the present invention is not limited to the above exemplaryembodiments, and can be modified without departing from the scope of theinvention.

In the above embodiments, active nominal scanning measurement has beenmainly described, but the “active nominal scanning measurement” may bereplaced with “passive nominal scanning measurement”.

1. A method for controlling a shape measuring apparatus which includes aprobe having a stylus head at a tip and a moving mechanism to move theprobe, and measures a shape of a workpiece by detecting contact betweenthe stylus head and a surface of the workpiece, the method comprising:allowing a user to select a shape of an object to be measured from ageometric shape menu prepared in advance; allowing the user to select ameasurement path from a measurement path menu prepared in advance;calculating, based on the selected geometric shape and the selectedmeasurement path, measurement points and a normal line direction at eachof the measurement points on the workpiece using a calculation formulaprepared in advance; and calculating a path for scanning measurement tomove while scanning a sequence of the measurement points, and performingthe scanning measurement to scan the path for the scanning measurement.2. The method for controlling the shape measuring apparatus according toclaim 1, the method further comprising: allowing the user to input,according to the selected geometric shape, a parameter to specify thegeometric shape; allowing the user to input, according to the selectedmeasurement path, a parameter to specify the measurement path; andcalculating, based on the selected geometric shape, the input parameterof the geometric shape, the selected measurement path, and the inputparameter of the measurement path, measurement points and a normal linedirection at each of the measurement points on a workpiece using acalculation formula prepared in advance.
 3. The method for controllingthe shape measuring apparatus according to claim 1, wherein thegeometric shape menu includes, at least, a sphere, a columnar body, acone body, and a plane.
 4. The method for controlling the shapemeasuring apparatus according to claim 1, wherein the measurement pathmenu includes, at least, a spiral and a sine curve.
 5. A non-volatilerecording memory containing a control program for a shape measuringapparatus causing a computer to execute a method for controlling theshape measuring apparatus according to claim 1.